A lost, blind kangaroo (Skippy) starts in position (0,0) of a grid, and is trying to get home, which happens to be at cell (dimension - 1, dimension - 1). His strategy is to take random hops either Direction::NORTH, Direction::SOUTH, Direction::EAST or Direction::WEST (with equal probability), without exiting the grid of course.

The question is, will this strategy get Skippy home, or will he hop around the grid forever?

More at: Part I: Basic Simulation

• Java 10+
• Ruby 2.7+

• Run tests: mvn test
• Run the program: mvn exec:java "-Dexec.mainClass=org.my_projects.skippy.Main"

• Install dependencies: ./bin/setup
• Run tests: bundle exec rake
• Run the program: ruby ./bin/console

Enter dimension of the grid (>=1):
100
Oops, hit the boundary: (-1, 0)
Oops, hit the boundary: (-1, 0)
Hopped to: (1, 0)
Hopped to: (1, 1)
...
Hopped to: (97, 99)
Oops, hit the boundary: (97, 100)
Hopped to: (98, 99)
Hopped to: (98, 98)
Hopped to: (98, 99)
Oops, hit the boundary: (98, 100)
Hopped to: (99, 99)
Finished in 119044 hops!

Die statistics:
Total throws: 119044
North: 24.9% South: 25.1% East: 25.1% West: 25.0%

• Grid is a container with items on it. It provides methods for updating and retrieving item locations (place_item, move_item, get_item_location) and makes it impossible for items to exit the grid (OutOfBoundsError)
• Skippy is an instance of Kangaroo. He is responsible for finding his way back to home (find_home). Kangaroo encapsulates this strategy: kangaroos roll the die and hop around the grid, instead of someone else rolling the die and making them hop.
• Die is a Singleton: we only need one die and one type of die in this exercise. It records its history and prints its own statistics.
• Classes are grouped into 3 modules: Skippy::Direction, Skippy::Grid and Skippy::Kangaroo
• The outputs of this program are because of Skippy chortling or the die printing its statistics.

• https://en.wikipedia.org/wiki/Markov_chain